1

Punch-through Jets in A+A Collisions at RHIC/LHC

Han-Zhong ZhangInstitute of Particle Physics, Huazhong Normal University, China

Collaborators: J. Owens, E. Wang and X.-N. Wang

Quark Matter 2008 Feb. 4-10 , 2008

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I. IntroductionII. Fragility of single/dihadron suppression factorsIII. Single/dihadron spectra at RHIC/LHCIV. Azimuthal angle anisotropy of single/dihadron

spectra at RHIC/LHCV. Conclusions

Outline

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I. Introduction

What happens for a jet propagating inside QGP?

Jet quenching:

The hard jet loses a significant amount of its energy

via radiating gluon induced by multiple scattering.

hadrons

q

q

hadrons

leadingparticle

leading particle

N-N collision

hadrons

q

q

hadrons

Leading particle suppressed

leading particle suppressed

A-A collision

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Jet Quenching effect in AA is incorporated via modified fragmentation functions.

FFstd

dPDFsT

dydp

dAB

T

AA

ˆ2

Nuclear geometry

A NLO pQCD parton model with jet quenching in A+A

Partondistribution

functions

NLO cross

sections

(X. -N. Wang , PRC70(2004)031901)),(

)],(/),()[1(),,(

2'0/

/

2'0/

'2'0

/

'/2

/

cchL

gghc

gcch

c

cLccch

zDe

zDz

zLzD

z

zeEzD

,//),/( ''cTgcTcTc EpLzEppz

Jet energy loss

5

Parton jet energy loss per unit length:

),(5.0

),/5.7/()6.1/( 02.1

01

partpartd

NsdN

dNEE

dL

dE

E. Wang , X. -N. Wang , PRL87(2001)142301)

B. B. Back for PHOBOS, nucl-ex/0604017v1

),(

),(

0

0

part

part

Nsf

Nsf

Initial gluon density coefficient

Energy loss parameter

),(5.0

),(

00

partpart

part NsdN

dNNsf

(a parameterization form of theory calculations)

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7

II. Fragility of single/dihadron suppression factors

Simultaneous fit of single/dihadron spectra

In most central Au+Au

dihadronsingle hadron

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2 -fit to both suppression factors

95.045.0

158

T

trigT

z

GeVp

GeVpT 204 for single

for dihadron

fmGeV /1.25.10 H. Zhang, J.F. Owens, E. Wang and

X.-N. Wang , PRL 98(2007)212301

Iaa robust when Raa fragile at RHIC

Sharp concave

Flat concave

in most central Au+Au

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Surviving jets: close and perpendicular to the surface

Surviving dijets: close and tangential to the surface +

punch-through dijets

dihadron

Color strength: yield per unit area

Thickness of the outer corona

single hadron

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2 -fit to all single hadron Raa factors in Au+Au with different centrality bins at RHIC energy

HIJING shadowing + JQ EKS98 shadowing + JQ

),(5.0

),(),,(0 partpart

partpart NsdN

dNNsfNsf

Energy loss parameter

1)397,200( GeVfNormalized in most central Au+Au at 200GeV

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III. Single/dihadron spectra at RHIC/LHC

punch-jets

Surface emission bias

fmGeVFixed /0.50

dihadron

single hadron

At LHC

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Comparisons for shadowing in single hadron spectra in p+A

At RHIC At LHC

4 kinds of shadowing parameterizations, (1)HIJ (S.-Y. Li and X.-N. Wang, PLB527(2002)85-91)

(2)EKS (K.J. Eskola, V.J. Kolhinen and C.A. Salgado, Eur. Phys. J., C9 (1999) 61)

(3)nPDF (M. Hirai, S. Kumano, and T.-H. Nagai, PRC70, (2004) 044905)

(4)nDS (D. de Florian, R. Sassot, PRD69(2004) 074028)

0 Ap

No Quenching! Only shadowing!

Shadowing depends on impact parameter in pA collisions.

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Single/dihadron spectra with different shadowing in A+A at RHIC

Single/dihadron Raa/Iaa are all insensitive to different shadowing at RHIC

dihadronsingle hadron

At RHIC

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Single/dihadron spectra with different shadowing in A+A at LHC

Single hadron Raa insensitive to different shadowing.

Dihadron Iaa sensitive to different shadowing.

At LHC

dihadronsingle hadron

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1) Initial partons participating in strong interaction in central region should be associated with stronger shadowing effects than those initial partons in the outer layer of the system.

2) Because of surface emission bias, single hadron Raa is insensitive to shadowing at RHIC/LHC.

3) Punch-through jets are created from central system region, and where the shadowing is stronger.

4) Punch-through jets at RHIC are greatly suppressed, so dihadron Iaa is also insensitive to shadowing at RHIC.

5) Punch-through jets at LHC are released to dominate dihadron, so dihadron Iaa is sensitive to shadowing at LHC.

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IV. Azimuthal angle anisotropy of single/dihadron spectra at RHIC/LHC

v2 definitions in single/dihadron spectra

dyddpdd

dyddpddp

ThAA

ThAA

Th

2

2

2/

/)2cos()(

Azimuthal anisotropy is

probed by “single jets”.

For dihadron,

dddydydpdpd

dddp

dddydydpdpd

dddp

p

assotrigassoT

trigT

hhAAasso

T

assotrigassoT

trigT

hhAAasso

TtrigT

hh

)2cos(

)(2

Azimuthal anisotropy is

probed by “dijets”.

r

xy Trig

Asso

For single hadron,

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234.6partN 166.6partN

114.2partN 74.4partN

45.5partN 25.7partN

GeVpT 85

Azimuthal angle anisotropy

manifested by jet quenching in high p_T single spectra

jets

single hadron at RHIC

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Dihadron v2 > single hadron v2

single hadron v2

dihadron v2

For single hadron, the anisotropy is probed by quenched single jets which have a bias of surface emission.

For dihadron, the anisotropy is probed by quenched dijets which have a bias of tangential surface emission.

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v2@LHC > v2@RHIC

RHIC

LHC

single hadron v2 dihadron v2

LHC

RHIC

Initial gluon density at LHC > RHIC

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V. Conclusions

1) -fit to both single and dihadron suppression factors

provides a convincing evidence for the jet quenching

description. I_AA is robust to probe the dense matter

when R_AA is fragile.

2) Punch-through jets are found to dominate high p_T dihadron production in Pb+Pb at LHC. Dihadron Iaa at LHC is able to distinguish different shadowing parameterizations.

3) Dihadron v2 > single hadron v2 at RHIC/LHC,and v2@LHC > v2@RHIC for both single/dihadron.

2

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Thank for your attention!

谢谢！

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),(),/5.7/()6.1/( 002.1

01

partd

NsfEEdL

dE

1)397,200(),,(5.0

),(,00 GeVfNsdN

dNNsf part

partpart

PHOBOS , nucl-ex/0510042v1, nucl-ex/0604017v1

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),(0 partNsf

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Surviving jets contributing to hadron at RHIC

Only vertical surface emission for single hadron

b=0 AuAuat RHIC

single jetsdijets

Tangential surface emission + punch-through for dihadron

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0-10% 10-20%

20-30% 30-40% 40-50%

50-60%

2) Suppression factors vs centrality

0-5%

60-70% 70-80%

single hadron

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nuclear modification factor

dydpdN

dydpdpR

TNN

binary

TAA

TAA 2

2

/

/)(

|)(|)(),(max

min

22maxmin brtrrtbddbbN

b

b AAbinary

)(

2222

/13

)(br

partpart RrrdR

AbNN

dydp

bbd

bbdydp

dN

T

hAA

AAinT

hAA

2maxmin

maxmin2

),(

),(

1

the formula of spectra in AATp

dydpddpbT

dydpdbddpNR

TNN

TAA

TAA

T

partAA 22

222

/)(

/)(

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Invariant mass: 221

2 )( ppM

How to fix scales: M

trigTtrighAAtrigTtrig

assotrigTassoTtrighhAATtrigassotrigTtrig

T

hhAA

trigAA

TAA

TtrigTassoT

dydpddydp

ddydydpdpdpddydydp

dz

dN

NzD

ppz

/

/

1)(

,/

If no medium effects, )()()( TppTdAuTAuAu zDzDzD

(X. –N. Wang , PLB 595(2004)165

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The dihadron azimuthal distributions

trigTtrighAAtrigTtrig

assotrigTassoTtrighhAAassotrigTassoTtrig

hhAA

trigAA dydpddydp

ddydydpdpddydydpdp

d

dN

N /

/1

ddydydpdppp

bbd

bbddydydpdppp

dN

TTTT

hhAA

AAinTTTT

hhAA

212121

maxmin

maxmin212121 2

),(

),(

1

2

212

221

maxmin

maxmin212

221

),(

),(

1

dydydpdp

bbd

bbdydydpdp

dN

TT

hhAA

AAinTT

hhAA

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The ratio between the yield/trigger in AA and in pp:

trigpp

hhpp

trigAA

hhAA

trigpp

hhpp

trigAA

hhAA

yieldpp

partyieldAA

partAA

bb

NN

bNbN

D

NDNI

/

)(/)(

/

)(/)()()(

30

AAR

N

j TjEx

TjThAATj

ExAA

pN

pRpR

12

20

02

)()1(

)],()([)(

for

31

jets

|)(|)(

),,(|)(|)(),(2

2

brtrtdrE

rbEbrtrtdr

E

bE

BA

BA